Computer security is becoming an ever more important feature of computing systems. As users take their computers with them in the form of laptops, palmtops, and smart phones, it becomes desirable to lock such mobile computers from access by third parties. Also, as more computing resources on servers are made available over the Internet, and thus theoretically available to anyone, it becomes more important to ensure that only legitimate users, and not hackers or other fraudsters, are using the resources.
Computer security is commonly provided by requiring a user to submit credentials in the form of a password or pass code. For example, a mobile device may lock after a set number of minutes of inactivity, and may require a user to type a password that is known only to them in order to gain access to the services on the device (or may provide access to limited services without a password). In a similar manner, a web site may require a user to enter a password before being granted access. Also, certain web sites may require potential users to enter a term that is displayed to the users in an obscured manner so that automated machines cannot access the web sites for proper or improper purposes (e.g., to overload the web site servers). Such techniques may be commonly referenced as CAPTCHA's (Completely Automated Public Turing test to tell Computers and Humans Apart).